In the original paper[1]}, ESPRESSO, with a resolution of R=220.000 was considered. The initial contrast requirement of \(2\times 10^{-4}\)  (i.e. \(\rho _\odot = 10^{-4}\) ) was imposed by the limits in the current visible detectors RON and dark current, considering exposure times of 1h: going towards higher contrast would not improve the final SNR.
RISTRETTO is now designed with a goal R=140.000, meaning less pixels are required. Under the same assumptions made in [1]}, we show that for 1h integration time, the stellar signal will be equivalent to the detector RON if its coupling \(\rho _\odot \sim 3\times 10^{-5}\) . Therefore, it would be meaningful to attempt pushing contrast to such extreme value to decrease integration times by up to 1.7 (which corresponds to days in the case of Prox Cen b).
